This invention relates to the filling and hermetic sealing of plastic-bodied containers with hot liquid or semi-liquid products, and in particular to improvements in the methods and structures for accomplishing same without deformation to the side wall of the container or premature breaking of the seal.
Recently there has been a demand for a thermoplastic container for storing jams which must be heated to a liquid or semi-liquid state at temperatures of up to about 190.degree. F. to facilitate filling into the container, and must then be hermetically sealed with a heat sealed peelable closure disc. This container can be used to package foods commonly classified as hot fillable, such as jams, fruit juices, and others. By hot-filling at a temperature of 190.degree. F. the container and contents are sterilized and do not require additional preservatives. The higher the temperatures that must be used, the greater the likelihood of creating stresses on the container and/or seal because of high internal vacuums developed upon subsequent cooling of a product, primarily because of the condensation of steam in the head space of the sealed container. It is important that the side wall of the container be kept free of deformation or paneling while at the same time maintaining the hermetic seal to prevent spoilage of the product during shipping and storage.
In the past it has been known to construct a thermoplastic-bodied container for storing motor oils with a flexible bottom so that depletion of gaseous components causing a change in the internal pressure can be compensated for by the flexing action on the bottom as described in U.S. Pat. No. 3,409,167 to Blanchard. The container of that patent was formed with a relatively thick side wall and a relatively thin bottom wall to prevent paneling to the side wall while permitting flexing of the bottom wall, as set forth in column 4, lines 3-10 thereof, for example.